A nuclear power plant usually uses a closed containment to contain reactors and several important safety systems, in order to prevent radioactive substances from leaking into the surrounding area in case an accident occurs in the nuclear power plant.
If the nuclear power plant uses a safety cooling system based on the passive concept and a flow control system based on the automatic control principle, not only engineered safety features can be simplified, but also operator interventions can be reduced, and thus misoperation that may be produced can be reduced, and man-machine relationship can be improved, thereby improving the safety of the nuclear power plant.
In an existing nuclear power system, in general, a cooling liquid storage tank is arranged on a top of the containment. When an accident occurs in the nuclear power plant, the storage tank provides water source, and the water is sprayed onto an outer wall of the containment to form water film. In this way, the heat of and inside the shell of the containment is conducted out by evaporation of the water film and air convection, and an internal pressure inside the containment is reduced by cooling, thereby ensuring that the containment will not be damaged due to too high pressure.
However, the above design has the following technical problems: when the water film has not been completely evaporated, the water in the storage tank of the cooling system will continuously flow downwardly, then reach to a bottom of the containment, and finally be directly discharged, which cause a waste of the cooling liquid. Meanwhile, in order to ensure that the containment is sufficiently cooled, a cooling liquid storage tank having a relative large capacity (a relative heavy weight) is generally provided at the top of the containment, and the mounting and maintenance thereof are inconvenient. It is likely for the structure of the cooling liquid storage tank to be damaged and for the safety function thereof to be disabled in case of coming across extreme events such as earthquake, tsunami, tornado and the like.
Meanwhile, in the existing design, there is no control for the spray flow of the cooling liquid storage tank, or a temperature of the containment is monitored by a sensor and a corresponding control unit is provided to give instructions to control the flow of the cooling liquid inside the cooling liquid storage tank. For the former one, if the flow is too large, lots of the cooling liquid is wasted since the cooling liquid can not be made the best use of. For the later one, the operations for monitoring the temperature of the containment and controlling the flow of the cooling liquid need a support of the power source, which makes a design of the structure of the hardware more complicated; besides, when a lots of accidents occur, it is possible for the power source to be failed, and thus the cooling design described above cannot work normally.